New Process Control System Encodes Unique Elements Of Process Engineers' Knowledge

Often, plant controls are nothing more than a controller connected
to a dissolved oxygen (DO) probe, programmed by an installer that may know
little about the actual process. Sometimes a control system is nothing more
than some clever animation, pretty graphics, and switches on a computer screen.

The challenge is to design automation that provides real
value to the user. Process knowledge and understanding of its control should be
encoded into the software. The control system should enable the operator to get
better performance than with a manual system. It should also bring knowledge
otherwise unavailable to the operation of the plant.

USFilter's Envirex Products provides a control system
designed by process engineers. The proprietary software in the controller
encodes unique elements of knowledge of process. It is the result of many
decades of work in developing process expertise as well as many years of
research in understanding the process.

The principle features of the SmartBNR process control
system are: precise control of simultaneous nutrient removal in the
aerated-anoxic reactor; predictive aerator response to reactor conditions and
oxygen demand; integrated control strategy using both oxidation-reduction
potential (ORP) and DO in reactors in series; automated sludge wasting to
control to an optimum sludge age; automated response to stormflow conditions.

* Untended plant operation. Plants
that are not attended nights and weekends still

perform control
functions.

The main function of the system is to optimize oxygen
delivery to a process using aerated-anoxic reactor. It maintains precise
reactor conditions to reliably remove both nitrogen and phosphorus as well as
provide selection of microorganisms to minimize the chance of bulking and other
process problems.

An extensive program of research has enabled USFilter's
process engineers to understand reactor conditions based upon ORP and DO. They
have also learned of trends that signal process changes and potential
degradation before it occurs. With this knowledge, they have developed a
responsive system that predicts reactor behavior and changes conditions in
advance.

Aerated-anoxic processes, while only recently entering the
mainstream literature, have been the mainstay of Envirex aeration processes for
more than two decades. Aerated-anoxic allows for simultaneous removal of
nitrogen in a single reactor. It also allows for enhanced biological phosphorus
removal without the use of expensive and inefficient anaerobic tanks.

In one sense, the main function of activated sludge is to
turn soluble waste into biosolids. Control of the solids inventory in a process
is the key to running a plant well. The SmartBNR system measures the solids
inventory in the process and wastes sludge to maintain a constant target sludge
age. The operator selects the sludge age, and the system does the rest.

It constantly evaluates the sludge inventory and updates
wasting requirements. Wasting is automatically controlled to meet other process
requirements in the plant. For instance, the system can waste to maintain a
level solids loading (constant mass flow rate) to get the best performance out
of dewatering equipment and allow dewatering with little or no operator
attention.

The constant nightmare for the duty operator is the
stormflow situation. A rainstorm in the middle of the night often means a call
from an automatic dialer. The operator must run out to the plant and try to
keep his solids from washing out of the plant.

The SmartBNR system automates the stormflow mode of
operation. This ensures that no solids are lost over the clarifier weirs and
that the duty operator can get a good night's sleep (or at least can focus his
attention elsewhere).

This system can run any number and variety of control
functions and programs in the plant. An example: in a plant with an
equalization basin, the controller can measure the level in the basin and
adjust pump speed to meet process goals.

The SmartBNR system uses a panel PC running PlantScape®
Vista software, offered through a strategic partnership between USFilter and
Honeywell for the human/machine interface (HMI). Through proprietary software
design, the PlantScape Vista automatically shares all graphics and control
points with PlantScape SCADA. This significantly reduces the cost of the SCADA
system. In plants with other SCADA systems, the SmartBNR system can communicate
on any standard communication protocol.

About The Author:

John Sheridan has worked as a process engineer for USFilter's Envirex Products for the past seven years. He earned a master's degree in environmental engineering from Marquette University. For more information, go to www.usfilter.com[10], contact John Sheridan ([email protected][11].